17. Exercises

Calculate the kinetic energy of a car, of mass 1200 kg, travelling at 30 ms−1.

Calculate the kinetic energy of a ball, which has mass 250 grams, and which is travelling at 9 ms−1.

A ball, of mass 0.125 kg, is thrown so that its initial speed is 12 ms−1. As the ball moves upwards its speed decreases to 4 ms−1 when it is at its maximum height.

a) Calculate the initial kinetic energy of the ball.

b) Calculate the minimum kinetic energy of the ball.

c) Calculate the potential energy of the ball at its maximum height.

A brick, of mass 2 kg, is allowed to fall from rest at a height of 3.2 m. Find the kinetic energy and speed of the brick when it hits the ground;

a) assuming that no resistance forces act on the brick as it falls,

b) assuming that a constant resistance force of magnitude 10 N acts on the brick.

A rock, which has mass 3 kg, is thrown from a bridge over a river at speed of 3 ms−1. When it hits the water, it is moving at a speed of 15 ms−1.

a) Find the kinetic energy gained as the rock falls.

b) Find the potential energy lost as the rock falls.

c) Find the height of the bridge above the river.